As you’ve probably noticed, there are two common sizes of router bit shank, and two common sizes of router collet: 1/4" and 1/2". Why? A larger diameter shank is necessary to safely carry the mass of a large router bit. A large diameter shank is also less prone to vibration and consequently tends to yield a smoother cut. In certain applications, on the other hand, a 1/4" shank is either necessary or all that's required. The shank of a dovetail bit, for example, has to be narrow enough to fit through the opening in a guide bushing if it to be used with a standard dovetail jig.
Is there anything magic about the 1/4" and 1/2" inch diameters? Of course not. They’re just handy standard sizes to use so that everyone has bits with the same diameter shank in their toolbox. It’s a great system and we wouldn’t mess with it unless we had a very good reason – which brings us to Rockler’s new 8mm Dovetail Router Bit Upgrade.
In a delicate operation like cutting dovetails, where precision really counts, you want every advantage possible. By adding 25 percent to the typical 1/4" shank size, Rockler has come up with a dovetail bit that produces a consistently smoother cut, but still fits comfortably inside a standard guide bushing. The kit comes with the three bits used most often for dovetailing and an adapter that fits in a 1/2" collet. It’s a small investment that’s likely to have a big impact on your dovetail cutting accuracy.
For more on 1/2" vs. 1/4" router bits, read on. Two experts in the field cover the basics in their response to a Woodworker’s Journal eZine reader’s question.
Q. My new Porter Cable router comes with two collets, 1/4" and 1/2". What is the advantage of the 1/4" size over the 1/2", or vice versa? It seems that the larger would be stronger, but I think there must be another reason for manufacturing the two sizes. I would like to have an idea of what to get as I start to build a library of bits. Right now, I will be doing light work, but in the months ahead, my tools will be used almost daily, so I will need some durable stuff.
A. Michael Dresdner: "Some bits don"t come in 1/2" shank format, and some buyers already have many 1/4" shank bits from other router purchases. Simply put, the 1/4" collet allows you versatility. Think about a flush cutting bit or "pattern" bit with the bearing on the shank above the cutter. It has a bearing pressed over the shank, and its outside race is the size of the cutter."
A. Ellis Walentine: "Many routers come with two collets so they can accommodate the two most popular bit shank diameters, 1/4" and 1/2". The shank diameter is based loosely on the size and weight of the bit. Heavier and larger-diameter bits have 1/2" shanks, to protect them against bending or breaking during heavy routing. Some small to medium bit sizes and profiles are available with either size shank. Generally, you will get less vibration with the 1/2" shanks, but 1/4" is available so you can run these bits in smaller routers that may have only 1/4" collet capacity."
A. Lee Grindinger: "You"re right, the larger diameter is stronger and generally results in less chatter due to its increased rigidity. However, there are times a 1/4" shank is more practical. Most dovetail jigs use template guides and these guides are sized so only the 1/4" shank will fit through the hole. Smaller bits, like 1/8" straight bits are sometimes offered only in 1/4" shanks. So, keep the small collet but do buy the 1/2" bits when possible or practical."
From the Woodworker's Journal eZine archives